Polarization Transfer in Weak Pion Production off the Nucleon

TL;DR

This paper investigates polarization transfer observables in weak pion production off nucleons, highlighting their sensitivity to background models and the interference between resonant and nonresonant amplitudes at neutrino energies around 1 GeV.

Contribution

It provides detailed calculations of polarization components in pion production models, revealing their dependence on background assumptions and interference effects.

Findings

Normal polarization components are influenced by RES and NB interference.

The sign of the lepton's normal polarization component is determined by amplitude signs.

Polarization observables are sensitive to nonresonant background models.

Abstract

Polarization transfer (PT) observables in the single pion production induced by the charged current interaction of the neutrino with the nucleon are examined. The polarization components of the final nucleon and the charged lepton are calculated within two models for the pion production. The predictions are made for neutrino energy of the order of 1~GeV as well as for the T2K energy distribution. It is demonstrated that the PT observables, the degree of polarization and the polarization components of outgoing fermions, are sensitive on assumptions about the nonresonant background model. In particular it is shown that the normal components of the polarization of the outgoing nucleon and the lepton are determined by the interference between the resonant (RES) and nonresonant (NB) amplitudes. Moreover the sign of the normal component of the polarization of the charged lepton is fixed by the relative sign between the RES and the NB amplitudes.